/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Lily
 * Date: 2024-09-21
 * Time: 14:25
 */
public class matrix_BlockSum {


    /*
     * 给你一个m x n的矩阵mat和一个整数 k ，请你返回一个矩阵answer，
     * 其中每个answer[i][j]是所有满足下述条件的元素mat[r][c] 的和：
     * */
    public int[][] matrixBlockSum(int[][] mat, int k) {
        int m = mat.length, n = mat[0].length;


        int[][] dp = new int[m + 1][n + 1];
        for (int i = 1; i < m + 1; i++) {
            for (int j = 1; j < n + 1; j++) {
                dp[i][j] = dp[i - 1][j] + dp[i][j - 1] - dp[i-1][j-1] + mat[i-1][j-1];
            }
        }

        int[][] ret = new int[m][n];
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                int x1 = Math.max(0, i - k)+1, y1 = Math.max(0, j - k)+1;

                int x2 = Math.min(m - 1, i + k)+1, y2 = Math.min(n - 1, j + k)+1;

                ret[i][j] = dp[x2][y2] - dp[x1-1][y2] - dp[x2][y1-1] + dp[x1-1][y1-1];
            }
        }

        return ret;
    }
}
